1. Field of the Invention
The present invention relates to an optical recording/reproducing apparatus, which is particularly suitable for recording/reproducing information on/from a write once type optical disc.
2. Description of the Related Art
Recording media (optical discs) currently in use are classified into three major types as follows: a read only type medium such as a Compact Disc-Read Only Memory (referred to as CD-ROM) or a Digital Versatile Disc-Read Only Memory (referred to as DVD-ROM); a rewritable type medium such as a Compact Disc-ReWritable (referred to as CD-RW) or a Digital Versatile Disc-ReWritable (referred to as DVD-RW); and a write once type medium such as a Compact Disc-Recordable (referred to as CD-R), a Digital Versatile Disc-Recordable (referred to as DVD-R), or a Digital Versatile Disc+Recordable (referred to as DVD+R) . Although write once type media such as CD-R, DVD-R, and DVD+R can each be written only one time, those media are cheep in comparison with rewritable type media and also maintain high compatibility with read only type media such as CD-ROM and DVD-ROM.
A write once type medium has a power calibration area (referred to as PCA) for adjusting laser power at an innermost circumference portion of the disc. Normal recording/reproducing operation is performed after laser power is adjusted using the PCA. In many cases, however, a conventional write once type recording medium uses only the PCA as a laser power adjusting area to maintain complete compatibility with a read only type medium. In those cases, there arises a problem in that recording operation is not performed after the PCA is used up, and therefore medium usability reduces. Such a problem is anticipated to be more serious with increasing capacities of write once type media.
For example, Japanese Non-examined Patent Publication No. 2002-175624 discloses a technique in which a laser power adjusting area (outer power calibration area) is provided in advance at an outermost circumference portion of a write once type medium and the laser power is appropriately adjusted using the adjusting area where required. According to this technique, adjustment of laser power using the outer power calibration area other than ordinary PCA can be performed, whereby the medium usability is improved when compared with the above-mentioned cases.
However, since an outer power calibration area is invariably provided in a write once type medium, this adjusting method cannot provide the write once type medium with capacity compatibility with a read only type medium in the case where both the media have the same disc diameter. There also arises a problem in that recording operation is not performed after the outer calibration is used up as with the above-mentioned case, and therefore medium usability reduces.